High-power white LED devices whose application to generic illumination has been studied demand encapsulation materials having excellent light resistance and heat resistance. In recent years, so-called “addition curing type silicone” has been heavily used.
This addition curing type silicone is obtained by thermal curing of a mixture mainly composed of a silicone derivative having vinyl groups on a main chain thereof and a silicone derivative having SiH groups on a main chain thereof in the presence of a platinum catalyst. For example, Patent Document 1 discloses a resin composition which provides a cured material having excellent transparency and insulating characteristics by introducing an organopolysiloxane into a composition to set the molar ratio of silicon-bonded hydrogen atoms in the composition to alkenyl groups to a specific range.
Patent Document 2 discloses a resin composition containing a silicone resin having at least two silicon-bonded alkenyl groups in one molecule thereof and an organohydrogensilane and/or an organohydrogensiloxane having at least two silicon-bonded hydrogen atoms in one molecule thereof.
Patent Document 3 discloses a composition which provides a cured material having an excellent strength by using a straight-chain polyorganohydrogensiloxane having a silicon-bonded hydrogen atom (a Si—H group) midway of a molecular chain in combination with a straight-chain polyorganohydrogensiloxane having Si—H groups at both ends of a molecular chain in specific amounts.
On the other hand, a high active platinum catalyst is generally used in the addition curing type silicone resin. Accordingly, when a curing reaction once starts, it is extremely difficult to stop the reaction halfway. It is therefore difficult to form a semi-cured state (stage B). Then, it has been known that addition of a phosphorus compound, a nitrogen compound, a sulfur compound or an acetylene as a reaction inhibitor is effective, in order to decrease the catalytic activity of the platinum catalyst (for example, see Patent Document 4).
Patent Document 1: JP-A-2000-198930
Patent Document 2: JP-A-2004-186168
Patent Document 3: JP-A-2008-150437
Patent Document 4: JP-A-6-118254